Load balancing full opening and rotating blowout preventer apparatus



Jan. 27, T970 H. w. LOAD BALANCING FULL AN-D ROTATING ARATUS June 7.1967 PENING EVENTER APP .ZJONES a I m KY V 55/ m. i u mummy/457 BLOWOUTPR Filed INVENTOQ. HOWARD W fines /WM,%,;M aw:

United States Patent U.S. Cl. 277-31 4 Claims ABSTRACT OF THE DISCLOSUREA blowout preventer apparatus for sealing off well pressure about arotating kelly or other rotating well drilling or production tool runtherethrough where a full opening packer element is rotatably mounted bya load balancing mounting frame journaled on hearing means equallyspaced outboard of the packer element. A rotating packer mounting framewith a configuration developed by rotating a vertically disposedinwardly opening hat section about a central axis receives and mounts anannular resilient packer element recessed within the central segment ofthe frame, the packer element having a non-deformed inner diametergenerally as large as the diameter of the preventer apparatus throughbore through which the kelly or other tools are run, with circularbearing means recessed within the apparatus bore and outboard of thepacker element in association with tubular vertical extensions of theframe above and below the frame central segment, and packer pressurizingmeans for compressing the packer element from a recessed full openedposition into the apparatus bore, inwardly of the apparatus, to sealabout the kelly or other well tool therein while rotating therewith.

BACKGROUND OF THE INVENTION This invention relates in general torotating blowout preventers used for sealing olf well pressures aboutrotating well drilling or production tools. More particularly, thisinvention relates to an improved full opening and load balanced blowoutpreventer adapted to seal about irregularly configurated well tools, asthe kelly employed in well drilling operations, while rotatingtherewith, which need not be removed from the well apparatus to allowthe running of tools into and out of the well and which balances theloading transmitted from the packer element through the rotating packermounting frame into the surrounding blowout preventer housing.

In conventional well drilling operations, it is common to drill the wellby rotating a drilling bit on the lower end of drill pipe run down intothe well by means of a kelly operated at the upper end of the drill pipeat the drilling rig. The kelly normally has a hexagonal or othernon-round or irregular cross-sectional shape to facilitate its rotationby conventional driving apparatus at the drilling rig. In order tocontrol the flow of drilling fluids normally employed in conventionaldrilling operations, as well as to contain well pressures therein, it isnecessary to effect a tight fluid seal about the rotating kelly by meansof a rotating blowout preventer apparatus during the drillingoperations. The kelly and the associated drill pipe are alsoperiodically raised upwardly through the blowout preventer to facilitatethe insertion of additional drill pipe in order to continue furtherdrilling operations. The blowout preventer sealing element is thereforesubjected to radially directed loading due to the rotation of the kellyabout which it is compressed as well as lateral movement of the kellyduring the drilling operations plus vertical or thrust loading due tothe internal well pressures 3,492,007 Patented Jan. 27, 1970 as well asthe vertical movement of the kelly against which the sealing element istightly compressed.

In prior blowout preventer devices devised to seal about irregularlyconfigured well tools such as the kelly employed in drilling operationsunder the conditions above described, the sealing or packer elements andthe associated mounting means for rotatably mounting the sealing orpacker elements have not allowed the full opening of the preventerapparatus bore to allow the running therethrough of other well toolshaving a diameter larger than that of the kelly or drill string. It hastherefore been necessary to remove the blowout preventer sealing elementand its mounting frame whenever such larger diameter running tools areto be run into the well. Also, such prior art blowout preventers, inattempting to obtain a tight seal about a rotating irregularlyconfigured drilling or production tool run therethrough have failed toprovide mounting means for the packer element which Will balance orequally distribute loading from the packer element into the surroundinghousing. Such unbalanced loading by the packer element upon its rotatingmounting means causes accelerated wearing of the associated bearing orjournal means shortening the working life of the blowout preventerapparatus and perhaps even producing failures during critical and veryexpensive well drilling or producing operations.

It is therefore the primary object of the present invention to discloseand provide a rotating blowout preventer apparatus which includes a fullopening load balanced packer element and associated mounting meanswherein the packer element when not under pressure opens to the fulldiameter of the apparatus through bore, approximately equal to thecasing bore upon which the apparatus is mounted, and which can be easilycompressed about a tool run therethrough and in a rotating sealingengagement with such tool balance and equally distribute loading on thepacker from the associated tool into the surrounding apparatus housing.

It is another object of the present invention to disclose and provide afull opening rotating blowout preventer apparatus for use in welldrilling and producing operations wherein a housing having a verticalbore therethrough is provided with an enlarged internal bore segment, anannular resilient packer element is provided with a non deformed innerdiameter generally as large as the smallest housing vertical bore,packer mounting frame means are provided for mounting the packer elementwithin the housing enlarged bore segment recessed relative to thehousing vertical bore and pressurizing means are provided forcompressing the packer element from its non-deformed full bore openposition within the housing enlarged bore segment toward a full closedposition about a well too] or tubing run through the housing verticalbore.

It is a further object of the present invention to disclose and providea blowout preventer apparatus as in the foregoing object wherein thepacker mounting frame means is journaled upon vertically spaced circularrace bearings provided within the housing at two load bearing areasgenerally equally spaced above and below the packer element, i.e.outboard of the packer element, to balance and equally distributeloading from the packer element via its frame mounting means into thesurrounding apparatus housing.

It is a still further object of the present invention to disclose andprovide a rotating blowout preventer apparatus for use in well drillingand producing operations characterized by its load balancing outboardbearing means wherein a housing having a generally vertical boretherethrough to receive well drilling or production tools is providedwith a resilient packer element and frame means for mounting the packerwithin the housing and particularly wherein at least two circularbearing means are mounted within the housing for rotatably mounting theframe and associated packer element within the housing, such bearingmeans being generally equally spaced above and below the packer elementand in generally vertical alignment with each other to engage verticalextensions of the frame means above and below the packer means generallyoutboard of the packer element in order to balance loading from thepacker element through the frame means and bearing means into thesurrounding apparatus housing.

SUMMARY OF THE INVENTION Generally stated, the present invention attainsthe foregoing objects through the provision of a housing including abody portion having a vertical bore therethrough with an enlargedcentral bore segment and a head portion to removably receive kelly anddrive bushings associated with the kelly run down through the housing.An annular resilient packer element having a non-deformed inner diametergenerally as large as the diameter of the body bore is provided so thatlarge diameter tools capable of being run through the body bore also canbe run through the full open packer element without need for removingthe packer element and its associated mounting means. The packermounting frame means provided rotatably mount the packer element withinthe body enlarged central bore segment in a recessed relation to thebody bore when in full open non-deformed state. Pressurizing means areassociated with the housing and are operable through the rotatingmounting frame in order to cause compression of the rotatable packerelement about the kelly or other tool run therethrough. In order tobalance the loading generated between the rotating kelly and packerelement tightly compressed thereabout, the packer mounting frame ismounted by circular race bearing means in two load bearing areas spacedabove and below the centrally mounted packer element, the bearing meansbeing termed generally herein as outboard bearing means. Preferably,such outboard bearing means are equally spaced above and below thepacker element in association with vertical extensions of the framemeans in order to balance the loading transmitted from the packerelement into the housing means. Also, su-ch outboard bearing means arepreferably disposed in recessed portion of the housing through bore atlocations in as close proximity to the housing bore as is possible whilestill allowing for a full opened passage through the associated framemeans with an internal diameter thereof approximating that of the bodybore therebelow.

The rotating blowout preventer, according to the present invention,therefore has the advantages of being full opening to allow the runningof large diameter tools therethrough without the need for removing thepacker element and its associated rotating frame mounting means. Theframe mounting means and the associated outboard bearing means balanceand distribute loading from the packer element evenly into the housingabove and below the packer element during the adverse loading conditionsnormally encountered during the complex rotational, vertical and lateralmovement of the kelly during drilling operations with the packer elementtightly compressed thereabout. These, as well as various additionaladvantages and objects of the present invention, will become apparent tothose skilled in the art from a consideration of the following detailedexplanation of 'an exemplary embodiment of a load balanced full openingand rotating blowout preventer apparatus according to the presentinvention. Reference will be made to the appended sheet of drawings inwhich:

There is shown a vertically sectioned perspective view of an exemplaryembodiment of the load balanced full opening and rotating blowoutpreventer apparatus according to the present invention with an exemplarywell drilling tool shown therein in phantom line.

Referring to the drawing, the rotating blowout pre- 4 venter apparatusof the preferred exemplary embodiment includes generally a housing,indicated generally at 10, within which an annular resilient packerelement, indicated generally at 40, is rotatably mounted by packermounting frame means, indicated generally at 30, with associatedoutboard bearing means indicated generally at 50 and 60, respectively.

In the preferred exemplary embodiment, the blowout preventer housing,indicated generallyat 10, includes a body portion 11 having a lower bodyflange 12 for mounting the housing on appropriate associated welldrilling and/or producing equipment. Housing body 11 has a verticalthrough bore 13 extending upwardly from bottom flange 12. The body boreis enlarged at the upper portion of body 11, centrally of the housing toprovide a central bore segment 14. In the preferred exemplaryembodiment, the enlarged central bore segment 14, formed by thesurrounding body side wall and the body web 15, provides an upwardlyopening cavity to receive the annular resilient full opening packermeans, indicated generally at 40, and its associated rotating mountingframe, indicated generally at 30.

A head or cap flange 16 is provided to enclose the central bore segmentor cavity 14 after the assembly of the resilient packer means and itsassociated rotating mounting frame. Head 16 may be removably assembledto the body 11 by means of conventional bolts 17 securing the outerflange portion 18 to the body side wall as seen in FIG. 1. Head 16 alsohas a vertical bore therethrough to receive kelly and drive bushings ashereinafter explained, the head or cap flange and body 11 therebyforming, in the preferred exemplary embodiment, a drum-like housinghaving a vertical through bore and a recess or enlarged central boresegment.

During expected drilling or production operations with the preferredexemplary embodiment of blowout preventer, it is expected that fluidssuch as drilling mud will be flowing through the housing bore 13 viaside port 19. In drilling operations, a kelly and associated tubing arerun down through the housing bore with the drilling fluids passingthereabout through bore 13 and side port 19. It is the function of theblowout preventer to close off the vertical bore through the housingabove side port 19 by means of a resilient packer means, as the packerindicated generally at 40 in FIG. 1. In order to reduce the wear on theresilient packing means, the packing means is adapted to rotate with thetubing or irregularly shaped kelly as hereinafter explained.

As seen in the upper portions of FIG. 1, a split kelly bushing 20 isprovided including a left bushing half 21 and a right bushing half 22fitted within a drive bushing 23 and seated therein on the drive bushingledge 24. A pair of splines, as spline 25, are provided in the drivebushing to transmit torque to the split kelly bushing halves therein. Aconventional snap ring retainer 26- is also provided. The kelly 27 isshown in phantom line run down through the split kelly bushing 20 andpassing through the vertical bore down through the blowout preventerhousing, indicated generally at 10. As hereinafter explained, rotationof the irregularly shaped kelly 27 is transmitted through the kellybushing 20 and drive bushing 23 to a a rotating frame means mounting theresilient packer means, according to the present invention, within theblowout preventer housing.

Rotating packer mounting frame means are provided, according to thepresent invention, to mount a full opening rotating packer means,indicated generally at 40, within the housing in a load balancingrelationship with the housing. In the preferred exemplary embodiment,such rotating packer mounting frame means includes a frame means,indicated generally at 30, which has a configuration which is developedby rotating a vertically disposed inwardly opening hat section about theaxis of the housing bore. Such configuration includes a centraldrum-like body portion 31 having upper and lower spaced, parallel walls32 and 33 interconnected by the circular vertical outer wall or web 34.Vertical and oppositely extending tubular extensions or flanges 35 and36 extend vertically upwardly and vertically downwardly of the portedframe walls 32 and 33, respectively. The central drum-like body portion31 is adapted to fit within the central enlarged 'bore segment 14 of thehousing, with sufficient clearance between the associated walls to allowrotation therebetween as well as the passage of hydraulic fluidtherebetween, as explained subsequently. The frame means, indicatedgenerally at 30, is adapted to be rotated by drive bushing 23 throughthe interaction of the splined engagement between drive bushing 23 andthe frame means upper tubular extension 35, as by tongue or key portion28 on drive bushing 23 received in the spline or keyway 37 in tubularextension 35.

An annular resilient packer element, indicated generally at 40 in thepreferred exemplary embodiment, is provided within the improved blowoutpreventer according to the present invention with a non-deformed innerdiameter generally as large as the diameter of the housing vertical boreto allow full opening of the packer element when not under closingpressures to facilitate the running of large diameter drilling orproduction tools through the blowout preventer packer means without theneed for its removal from the well apparatus. In the exemplaryembodiment, the full opening packer means includes an inner resilientpacker element 41 having an inner nondeformed diameter generally aslarge as the body bore 13, as seen in FIG. 1. Inner packer element 41 iscompletely received into the drum or recessed area of the rotatingpacker mounting frame means, indicated generally at 30, to be rotatablymounted and recessed within the central bore segment 11 of the housing,indicated generally at 10. In the preferred exemplary embodiment, anouter packer element or hydraulic fluid accumulator 42 is shown.Hydraulic fluid accumulator or retainer 42 is provided to prevent theloss of hydraulic pressuring fluid for pressuring the inner packerelement 41. Outer packer element 42 is shown retained within therotating frame means by means of a retainer 43 holding leg portions ofthe retainer in tight sealing engagement with upper and lower recessesformed in the rotating frame means. A port 44 is provided in theretainer to allow introduction of hydraulic pressuring fluid into theaccummulator or bag 42 to force the associated inner packer element 41inwardly of the housing against the kelly or other tool rotating thereinas shown in phantom lines in FIG. 1.

Packer pressurizing means for compressing the packer element 41 inwardlyof the frame means against an oil well tool or tubing run through thehousing vertical bore includes the housing inlet 29 to be connected to asource of hydraulic fluid under pressure, a main hydraulic pressurechamber, indicated generally at 45, formed between the rotating framemeans 30 and the surrounding housing bore 14 and the hydraulic fluidinlets, as inlet 46, in the packer mounting frame means. From theforegoing, it can be seen that hydraulic fluid under pressures exceedingthe well pressure in body bore 13 may be introduced into the housingfrom a source of such pressure fluid through port 29 into the mainpressure chamber formed between the rotating frame means and thesurrounding housing. Hydraulic fluid may then be directed from the mainpressure chamber, as chamber 45 within the central bore segment of thehousing, to the packer pressurizing chamber 47 formed within the packerframe means by the outer packer element or hydraulic fluid accumulator42, to the associated outboard bearing means, indicated generally at 50and 60, for lubrication purposes and, also, outwardly thereof to thespaced mechanical seal means indicated generally at *80 and 30,respectively.

Bearing means are provided within the housing for rotatably mounting thepacker mounting frame indicated generally at 30. As particularlycontemplated within the present invention, the full opening packerelement 41 and its associated rotating mounting frame are rotatablymounted by vertically spaced bearing means which are outboard of thepacker element, ie. the bearing means are vertically outwardly of thepacker element 41 within the blowout preventer housing, indicatedgenerally at 10. In the preferred exemplary embodiment, such outboardbearing means include the circular bearing means indicated generally at50 and 60 in FIG. 1. While tapered roller bearings are employed in thepreferred exemplary embodiment, other forms of circular bearings,including roller bearings and thrust bearings, may be employed.

'Upper circular bearing means, indicated generally at 50, of theout-board bear-ing means employed in the preferred exemplary embodiment,include an upper inner fixed race 51 and a lower inner fixed race 52mounted to the vertically upwardly extending tubular flange or extension35 of the packer mounting frame means, indicated generally at 30. Fixedinner races 51 and 52 provide inwardly inclined or convergent bearingsurfaces opposing a pair of bearing race surfaces provided upon theouter stationary race 53 with a plurality of tapered roller bearings 54and 55 therebetween. Outer stationary race 53 is seated within thehousing head or cap 16 upon a ledge 56 provided within the inner bore ofhead or cap 16. The lower inner rotating race 52 fitted about tubularextension 35 is seated upon a ledge 57 formed in the rotating frame atthe juncture between extension 35 and frame web 32. A retainer ring 58is mounted by threads 59 to the frame tubular extension 35 to retain therotating inner upper race 51 in assembled relation.

As seen in the upper portion of FIG. 1, a collar 70 may be adjustablyscrewed into a threaded recess72 provided in the boss 73 formedintegrally with head or cap 16. A depending annular flange 74 on collar70 may be employed to retain the upper bearing means outer race 53 inassembled relation with an upper recessed flange area of the collarretaining the upper se-al means, indicated generally at 80, in assembledrelation as hereinafter explained.

Lower circular bearing means, indicated generally at 60, include aninner rotating race 61, a stationary outer circular race 62 and aplurality of tapered roller bearings 63 therebetween. Inner race 61 isfixed upon the frame lower tubular extension 36, seating upon ledge 64formed in the frame at the juncture of extension 36 with frame web 33. Aretainer ring 65 adjustably mounted to the tubular extension 36 bythreads 66 is provided for retaining the rotating inner race assembledto the packer mounting frame, indicated generally at 30. Outerstationary race 62 is seated on a ledge 67 provided by an enlarged orrecessed portion of bore 13. Roller spacer means 68 are provided forspacing of the plurality of tapered roller bearings 63, the lower leg ofspacer 68 being seated upon the retainer ring 65.

The bore of head or cap 16 is enlarged sufliciently to allow positioningof the bearing means 50 in alignment with the bearing means, indicatedgenerally at 60, reoessed relative to the housing body bore 13. Thevertically spaced, outboard bearing means, indicated generally at 50 and60, are thus adapted to mount the rotating frame means within thehousing recessed relative to the vertical housing bore so that therotating frame and its associated packer means will not interfere withpiping or other large diameter tooling run through the blowout preventervertical bore. A particular advantage of the outboard positioning of thebearing means, indicated generally at 50 and 60, in the preferredexemplary embodiment is that the loading upon the frame means exerted bythe packer element 41, about the kelly 27 or other tool run through thehousing bore, is evenly distributed by the frame means to the spacedoutboard bearing means at two load hearing areas which are generallyequally spaced above and below the packer element. The use of taperedroller bearings as herein described allows for the balancing of thrustloading axially of the frame as well as balancing of the radiallydirected loading.

In the preferred exemplary embodiment, the hydraulic pressure fluidwithin pressure chamber 45 employed for pressurizing the packer element41 is also employed for lubricating the circular bearing means indicatedgenerally at 50 and 60. Sulficient clearance is provided between therotating frame means and the surrounding housing portions including bore14, housing web 15 and removable head or cap 16 so that the hydraulicfluid within chamber 45 may travel around the rotating frame to thecircular bearing means 50 and 60. In order to prevent loss of suchlubricating fluid for the bearing means, seal means are providedvertically outwardly of the bearings in association with the frameextensions 35 and 36 and the adjacent portions of the blowout preventerhousing, indicated generally at 10. In the preferred exemplaryembodiment, such seal means, indicated generally at 80 and 90, includemechanical seal means which comprise a stationary metal ring mounted tothe housing and a rotating metal sealing ring mounted to the rotatingframe means to bear in sealing engagement with the stationary ring.

For purposes of the present invention, any suitable seal means may beemployed for the sealing means indicated generally at 80 and 90respectively. The particular mechanical seal means herein disclosed havethe advantage of a long wearing life and form a part of the inventionand are more fully described in my co-pending application Ser. No.644,197 entitled Pressure Fluid System With Mechanical Seals for ARotating Blowout Preventer Apparatus filed concurrently with thisapplication, and now abandoned.

From the foregoing detailed description of an exemplary embodiment ofthe load balanced full opening and rotating blowout preventer, accordingto the present invention, it can be seen that the rotating packerelement, being full opening, need not be removed from the preventerapparatus and associated well apparatus in order to pass large diameterwell tools through the preventer housing, the housing body bore 13 beingapproximately the same diameter as the casing bore upon which it ismounted. The packer, through full opening into a recessed positionrelative to the housing through bore, can be selectively pressurizedwithin its mounting frame to be compressed about and rotate with a kellyor other tool run therethrough. Importantly, the loading on the packermounting frame arising because of the forces between the vertically andlaterally moving, as well as rotating, kelly and the packer, the fluidpressures between the packer and its frame mounting means and internalwell pressures are distributed in a balanced manner by the frame meansthrough its associated outboard thrust and radially loadable tapered,circular race, roller bearing means.

While a single preferred exemplary embodiment of the load balanced fullopening and rotating blowout preventer apparatus according to thepresent invention has been described herein in detail, it is to beunderstood that this disclosure is intended to be exemplary only and isnot intended to limit the scope of the invention which may include otherembodiments, adaptations and modifications thereof made within thepresent invention as defined and limited only by the following claims.

I claim:

1. An improved rotating blowout preventer apparatus for use in welldrilling and producing operations characterized by its load balancing,full opening rotating packer means, said preventer apparatus comprising:

a housing including a body portion and an overlying head portion, eachsaid portion having a generally vertical bore therethrough, said bodyportion including an enlarged central bore segment providing an upwardlyopening cavity in said body portion partially enclosed by said overlyinghead portion;

circular bearing means recessed within the bore of each of said body andhead portions, each of said bearing means including a stationary outerrace mounted to the associated housing portion, an inner rotating race,and movable bearing elements between said races;

an annular resilient packer element having a nondeforrned inner diametergenerally as large as the diameter of said vertical bore through saidbody portion;

packer mounting frame means for rotatably mounting said packerelementbetween said bearing means within said housing, said frame meansincluding a central vertically apertured drum portion in which saidpacker element is received and thereby mounted within said enlargedcentral bore segment and a pair of oppositely extending tubularextensions of smaller outer diameter than said drum portion, each ofsaid extensions extending outwardly of said drum segment and packerelement into engagement with said bearing means outboard of said packerelement and frame drum portion to rotatably mount said packer elementand drum portion recessed in said housing relative to said housing bore,said frame means having an inner through bore through said extensionsand drum portion having a diameter generally as large as the diameter ofsaid housing body portion vertical bore; and

packer pressurizing means for compressing said packer element inwardlyof said frame means against an oil well tool or tubing run through saidhousing vertical bore.

2. In a full opening rotating blowout preventer apparatus for use inwell drilling and producing operations having a housing having agenerally vertical bore therethrough with an inner enlarged boresegment;

an annular resilient packer element having a nondeformed inner diametergenerally as large as the diameter of said housing vertical bore andpressurizing means for compressing said packer from a nondeformed fullbore open position within said housing toward a full closed boreposition about a well tool or tubing run through said housing bore, theimprovement comprising the provision of:

packer mounting frame means including an enlarged central drum portionfor receiving and mounting said packer element within said housingenlarged bore segment and a pair of oppositely directed frame extensionshaving smaller outer diameters than that of said drum portion, saidextensions lying generally in said housing bore with said drum portionbeing recessed relative thereto into said housing enlarged bore segment;and

bearing means provided within said housing bore adjacent said enlargedbore segment for mounting said frame means by said tubular extensionsfor rotation within said housing with said drum portion and packerelement disposed between and recessed relative to said bearing means insaid housing.

3. A rotating blowout preventer apparatus for use in well drilling andproducing operations characterized by its load balancing outboardbearing means, said apparatus comprising:

a housing including a generally vertical bore there through to receivewell drilling or producing tools;

a resilient packer element and frame means for mounting said packerwithin said housing to be compressed about a tool run therethrough, saidframe means including vertically spaced and oppositely directedextensions; and

at least two circular bearing means mounted within said housing formounting said frame means, said bearing means being generally equallyspaced above and below the packer element received in said frame meansand in generally vertical alignment, each said bearing means receivingand rotatably mounting said frame means by engagement with a frame meansextension outboard f the packer element retained in the frame means.

4. A full opening rotating blowout preventer apparatus for use on a wellcasing in well drilling and producing operations which allows for therunning of large diameter tools through said casing without removal ofsaid apparatus, said blowout preventer apparatus comprising:

a housing including a vertical through bore having a diameter generallyequal to that of a well casing on which said housing is mounted and anenlarged central bore segment;

an annular resilient packer element having a nondeformed inner diametergenerally as large as the diameter of said housing vertical bore;

packer mounting frame means having a through bore generally equal tothat of said housing and an enlarged central drum portion in which saidpacker is mounted, Said frame means including opposed tubular flangeextensions extending axially outward of said drum section and packerwithin said housing bore;

bearing means provided in said housing bore adjacent said enlargedcentral bore segment for mounting said frame means by said tubularflange extensions being engaged in said bearing means with said framemeans drum portion recessed relative to said housing bore in saidhousing enlarged central bore segment to allow running of well toolshaving an outer diameter approaching that of said casing through saidhousing bore without removal of said packer element therefrom; andpressurizing means for compressing said packer from a non-deformed fullbore open position within said frame means toward a full closed boreposition about a well tool or tubing run through said housing bore.

References Cited UNITED STATES PATENTS 883,155 3/1908 Westinghouse 277612,176,355 10/1939 Otis 27731 2,192,805 3/ 1940 Seamark 27731 2,479,2658/ 1949 Roshong 27727 2,846,247 8/1958 Davis 16684 X 3,387,851 6/1968Cugini 277-2 SAMUEL ROTHBERG, Primary Examiner US. Cl. X.R.

